The simulation and experimental study of granular materials discharged from a silo with the placement of inserts
Shie-Chen Yang, Shu-San Hsiau
Department of Mechanical Engineering
National Central Uniersity,
Chung-Li, Taiwan 32054
Taiwan
Source : http://www.sciencedirect.com/science...
Abstract
The simulation method of DEM and experimental method are used to investigate the flow pattern of the filling and discharging
process for two-dimensional plane silos. Two kinds of inserts conical insert and BINSERTw. are used in the silo to change the flow
fields of the silo. The placement of inserts improves the flow behaviors of funnel flow type to mass flow type during discharging. The
wall normal stresses are influenced by the change of the flow type. The effects of using differently shaped inserts on the flow pattern and
wall stress are analyzed in this study. The controlling parameters include the silo half-angle, the orifice width, the shape of the insert and
the properties of the granular materials. The simulation and experimental results are in good agreement. q2001 Elsevier Science B.V. All
rights reserved.
Introduction
Considerable importance has been given in industries
these days for the handling of granular materials. Roughly
one-half of the products and about three-quarters of the
raw materials of chemical industry are in the form of
granular materials that are usually stored in silos or bunkers
w1x. Although the silo is widely used, the understanding of
the flow behaviors in the silos is not very established. In
fact, a general and approachable research for designing a
silo is not available. Fluidity of the entire materials in the
silo and the load distributions on the silo walls are the two
pertinent questions to be addressed while considering the
material discharge from the silo.
Two distinct flow types are conventionally recognized
for the silo discharge problem: mass flow type and funnel
flow for core flow. type w2x. If all the materials inside a
silo are in flowing condition during discharge, the flow
region is called mass flow, which is an ideal flowing style
for running a silo. On the other hand, if there are stagnant zones for called dead zones. near the silo walls where the
particles flow slowly or are stagnant, the flow type is
called funnel flow or core flow. The silo geometry and the
properties of the granular materials have important influences
on the flow pattern. A rigid insert is generally used
to improve the flowing performance and also to reduce the
wall stress, which may give rise to the stable arching or
dome formation during the discharging process w3,4x. Although
various types of inserts are used in industries, the
understanding of the mechanism with a fixed insert placed
in a silo is not known with certainty still. A method to
design a conical insert used in a conical hopper based on
the theory of characteristic line is proposed by Johanson
w4x. Johanson also suggested a critical height above the silo
outlet to reduce the size of stagnant zone observed in a
funnel flow hopper. Another type of insert is called conein-
cone insert BINSERTw., which is a hopper-like structure
allocated in the inclined hopper section in order to
change the flow pattern w5x.
The requirements of silo design are the flow problems
and the structural stability of the silo. The wall pressure of
bulk solid in a silo is different significantly to that of fluid
in a container. The wall stress in silos with no inserts has
been investigated both experimentally and theoretically for
many years w2,7–12x. But there were few literatures to investigate the wall stress in silos with inserts. Strusch and
Schwedes w12x experimentally investigated the triangular
insert loads and wall stress distribution on a model silo.
They also theoretically calculated the insert load by means
of the slice element method. Tuzun et al. w6x experimentally investigated the effects of triangular and square inserts
on the flow patterns within a tall bunker. They also
measured the wall normal and shear stress. The experimental
results were compared with the theories of continuum
modeling.
In numerical simulation, the discrete element method
DEM. proposed by Cundall and Strack w13x has been
successfully used to study the related problems of granular
materials. There are more related literatures regarding the
application of DEM to analyze the silo problems. For
example, Thornton w14x applied DEM model to record the
silo flow, to monitor the change of solid fraction distribution
and the discharging rate. Sakaguchi and Ozaki w15x
investigated the dynamic process of formation of arches,
plugging phenomenon, by experiments and DEM simulations.
Ristow w16x investigated the dependence of the discharging
process in a two-dimensional hopper on various
material and geometrical parameters.
In this paper, the DEM and experimental methods are
used to investigate the flow behavior of granular materials
discharging from a two-dimensional plane silo. The flow
patterns and the dependence of discharging rate, the wall
normal stress during discharging, are studied. The influence
of differently shaped inserts on the stagnant zone of
the silo is also analyzed in this study. The important
geometry parameters considered include the silo width D,
the orifice width D , the hopper half-angle a and the 0
shape of the insert.
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